1. Field of the Invention
The present invention relates to an ultrasonic search unit used for an ultrasonic diagnostic apparatus that scans an ultrasonic wave electrically or mechanically to display an ultrasonic diagnostic image.
2. Description of the Related Art
Conventionally, regarding an ultrasonic search unit of the abovementioned type, the configuration described in “Revised Medical ultrasonic equipment handbook (p. 42, FIG. 2.39), edited by Electronic Industries Association of Japan, April 1985: issued by Corona Publishing Co., Ltd.” is known. Hereinafter, a conventional ultrasonic search unit will be described.
FIGS. 7A and 7B schematically illustrate a configuration of a piezoelectric plate and acoustic matching layers of a conventional ultrasonic search unit and a method for producing the same. A piezoelectric plate 21 shown in FIGS. 7A and 7B converts an electric signal sent from an ultrasonic diagnostic apparatus (not shown) to a mechanical vibration. In order to transmit an ultrasonic signal sent from the piezoelectric plate 21 to a living body as a subject to be measured with good efficiency, a first acoustic matching layer 22 and a second acoustic matching layer 23 are bonded to the front surface of the piezoelectric plate 21 with adhesive layers 24. FIG. 7A shows an exploded view before the first acoustic matching layer 22, the second acoustic matching layer 23, and the piezoelectric plate 21 are bonded to each other. FIG. 7B shows a state where these components are bonded to each other with the adhesive layers 24.
An integrated configuration of the piezoelectric plate 21 and the acoustic matching layers 22 and 23 generally is called an acoustic element. An acoustic element of a conventional ultrasonic search unit converts an electric signal sent from an ultrasonic diagnostic apparatus into a mechanical vibration, using the piezoelectric plate 21. The mechanical vibration of the piezoelectric plate 21 is sent to a human body via the acoustic matching layers 22 and 23. An ultrasonic signal reflected from boundaries of respective tissues in the human body is converted into an electric signal by the piezoelectric plate 21 through a path opposite to that from the piezoelectric plate 21 to the human body. Thus, a tomogram of the human body is displayed on a display screen of the ultrasonic diagnostic apparatus.
JP7(1995)-12239 B describes an ultrasonic search unit using light-curable resin. The invention disclosed therein relates to a method for coating divided groove portions of an array-type ultrasonic search unit with light-curable resin, and does not relate to an acoustic matching layer or a method for producing the same.
JP5(1993)-15530 A describes that a light-curable resin is used as an acoustic matching layer, UV-transparent glass powder is mixed in the resin, and the resin is cured with UV-light.
In the above-mentioned conventional ultrasonic search units, it is difficult to form an acoustic matching layer with a desired thickness, which is made of a material having an acoustic impedance with an intermediate value between the acoustic impedance of the piezoelectric plate and that of the living body, for the purpose of transmitting a vibration of the piezoelectric plate to the living body with good efficiency,
More specifically, in the conventional configuration, in order to produce an ultrasonic search unit with a small variation in acoustic characteristics and high acoustic performance, it is required to provide an acoustic matching layer with a desired thickness, which necessitates the management of a treatment operation and a thickness with high precision by polishing or the like. Furthermore, in general, at least one acoustic matching layer previously formed is bonded with an adhesive, and the acoustic matching layer is bonded to the entire surface of the piezoelectric plate with an adhesive. Therefore, even if the acoustic matching layer is treated with high precision, air bubbles in the adhesive layer and a variation in thickness of the adhesive layer may cause a variation in characteristics and degradation of the entire ultrasonic search unit.